Piston: Service and Repair

Pistons and connecting rods, disassembling and assembling

Vehicles with engine code APH

Note:
Secure engine to engine bracket VW 540 on assembly stand when dissembling/assembling engine.

1. Piston ring
^ Offset gaps by 120°
^ Remove and install with piston ring pliers
^ "TOP" faces toward piston crown
^ Checking ring gap, Refer to Fig. 1
^ Checking ring to groove clearance, Refer to Fig. 2
^ 2 or 3 part oil scraper ring, mixed installations permissible
2. Piston
^ Checking, Refer to Fig. 3
^ Mark installation position and cylinder number
^ Arrow on piston crown points to pulley end
^ Install using piston ring clamp
3. Connecting rod
^ Only replace as a set
^ Mark cylinder number -B-
^ Installation position: Marking -A- faces toward pulley end
4. Connecting rod bearing cap
^ Note installation position
^ Installation position: Marking -A- faces towards pulley end
^ Mark cylinder number -B-
5. 30 Nm+1/4 turn (90°) further
^ Always replace
^ Oil threads and contact surface
^ To measure radial clearance tighten to 30 Nm but not further
6. Pressure relief valve, 27 Nm
^ Opening pressure: 1.3 to 1.6 bar
7. Oil spray jet
^ For piston cooling
8. Bearing shell
^ Note installation position
^ Do not interchange used bearing shells
^ Ensure retaining lugs fit tightly in recesses
^ Axial clearance New: 0.10-0.31 mm Wear limit: 0.40 mm
Check radial clearance with Plastigage:
^ New: 0.01-0.05 mm
^ Wear limit: 0.09 mm
^ Do not rotate crankshaft when checking radial clearance
9. Cylinder block
^ Checking cylinder bores, Refer to Fig.4
^ Piston and cylinder dimensions
10. Connecting rod bolt
^ Always replace
11. Circlip
12. Piston pin
^ If difficult to remove, heat piston to 60°C
^ Remove and install with VW 222a










Fig. 1 Checking piston ring gap

Special tools and equipment
^ Feeler gauges
- Push ring squarely from above down to approx. 15 mm from bottom end of cylinder.









Fig. 2 Checking ring to groove clearance

Special tools and equipment
^ Feeler gauges
- Clean groove before check.







Fig. 3 Checking piston

Special tools and equipment
^ Micrometer 75-100 mm
- Measure pistons approx. 10 mm from lower edge of skirt, at 90° to piston pin axis.
Deviation from nominal dimension max.: 0.04 mm





Fig. 4 Checking cylinder bores

Special tools and equipment
^ Internal dial indicator 50-100 mm
- Measure bores at 3 locations in both directions -A- across engine and - B- in line with crankshaft.
Deviation from nominal dimension max.: 0.10 mm

Note:
Measuring the cylinder bores must not be done when the cylinder block is mounted on a repair stand with adapter bracket VW 540, as incorrect measurements would then be possible.





Piston and cylinder dimensions (engine code: APH)
1) Dimension without graphite coating (thickness 0 02 mm). The graphite coating wears away.